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Does Low-Density Lipoprotein Cholesterol Influence the Relationship Between High-Density Lipoprotein Cholesterol and Cardiovascular Risk in Women?FREE

The full report is titled “Association of High-Density Lipoprotein Cholesterol With Incident Cardiovascular Events in Women, by Low-Density Lipoprotein Cholesterol and Apolipoprotein B100 Levels. A Cohort Study.” It is in the 6 December 2011 issue of Annals of Internal Medicine (volume 155, pages 742-750). The authors are S. Mora, J.E. Buring, P.M Ridker, and Y. Cui.

What is the problem and what is known about it so far?

Cholesterol and triglycerides are fatty substances known as “lipids.” Lipids travel through the bloodstream in the form of lipid-and-protein packages called “lipoproteins.” Low-density lipoproteins (LDLs) carry more cholesterol than do high-density lipoproteins (HDLs) and deposit it around the body. High levels of total and LDL cholesterol increase the risk for cardiovascular disease (CVD), including heart attack, arterial disease, heart failure, and stroke. In contrast, low levels of HDL cholesterol increase the risk for CVD.

Researchers also use apolipoprotein A-I and apolipoprotein B100 to evaluate CVD risk. Low apolipoprotein A-I levels and high apolipoprotein B100 levels increase the risk for CVD.

Why did the researchers do this particular study?

Research has not confirmed how different levels of LDL cholesterol influence the relationship between HDL cholesterol and CVD risk, particularly in women. It is also unclear how HDL cholesterol or apolipoprotein A-I levels are associated with CVD when apolipoprotein B100 levels are low (less than 0.9 g/L).

Who was studied?

26,861 female health care professionals who were enrolled in the Women's Health Study. Participants were healthy and at least 45 years of age at the time of enrollment.

How was the study done?

The researchers obtained lipid and apolipoprotein measurements from a blood sample that participants provided at the start of the study. They then sent the participants questionnaires about any CVD-related events. These events included nonfatal heart attack or stroke, angioplasty or coronary artery bypass grafting (CABG), or death from cardiac causes. Only confirmed events were included in the study.

What did the researchers find?

Over 11 years, 929 CVD events occurred; of these, 602 were heart attacks, angioplasties or CABGs, or deaths from cardiac causes and 319 were strokes. Regardless of LDL cholesterol level, lower HDL cholesterol or apolipoprotein A-I levels increased the risk for coronary events, and higher HDL cholesterol or apolipoprotein A-I levels decreased the risk. This relationship between HDL cholesterol and risk for coronary events persisted, even among study participants with naturally low LDL cholesterol levels and independent of other risk factors, such as smoking, high blood pressure, or diabetes.

Only participants in the lowest category of HDL cholesterol level (39.5 mg/dL or less) had an increased risk for stroke. Among women with low apolipoprotein B100 levels (less than 0.9 g/L), few events occurred and the researchers did not see any relationship between HDL cholesterol and CVD.

What were the limitations of the study?

The participants were at low risk to start with, so it is unclear whether the findings apply to less healthy, higher-risk persons, such as those taking lipid-lowering therapy. The study population included mostly white health care professionals.

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